Spin orientation in an ultrathin CoO/PtFe double-layer with perpendicular exchange coupling

We studied by soft X-ray absorption spectroscopy the magnetization axis in a 4 nm thin CoO (111) layer exchange-coupled to an ultra thin L10 PtFe layer with perpendicular magnetic anisotropy. The angular dependence of the linear magnetic dichroism at 10 K and the relative variations of the spectral features provide a full description of the spin orientation in this antiferromagnetic layer. The spins are found in the film plane, pointing along the 110 direction. This results is discussed in relation to the film strain and the preferential occupation of t2g orbitals. The strong orthogonal coupling between Co and Fe spins should be at the origin of the robustness of the exchange bias effect found in this bilayer system.